The intracellular development of Chlamydia psittaci and C. trachomatis strains will be investigated in vitro with two host cell types. Emphasis will be placed on evaluating the role of non-sedimentable products derived by incubating specifically sensitized lymphocytes and macrophages with chlamydial antigen. Chlymydial development will be compared in murine peritoneal macrophages and L cells (mouse fibroblasts) after exposure to products (lympokines) of immunocompetent cells. Biochemical changes in the host cells following stimulation or infection will be assessed. Determination of host cell metabolic parameters which specifically respond to the addition of lymphokines will be sought. The requirements for, and changes in, host cell macromolecular synthesis after stimulation will also be evaluated. The stage of parasite development inhibited by lymphokine action will be assessed and the potential for reactivation of chlamydial growth following stimulation will be tested. This project will provide information concerning the role of the cell mediated immune system in controlling chlamydial proliferation and in maintaining the persistent or chronic state.